1. Field of the Invention
The present invention relates to an ink, a method of reducing kogation on the surface of a heater for applying thermal energy to an ink, an ink-jet recording process, an ink-jet recording apparatus, a recording unit, and a method for lengthening the life of an ink-jet recording head.
2. Related Background Art
Various systems have heretofore been proposed on printing using an ink-jet system. Among others, an ink-jet system (the so-called bubble-jet system) described in, for example, Japanese Patent Application Laid-Open No. 54-51837 or the like, in which an ink is ejected as ink droplets by the action of thermal energy, features that the formation of a high-density multi-orifice in a recording head can be realized with very ease, high-quality images can be provided at high speed and very low cost, and printing can also be conducted on plain paper having no special coating layer. According to this system, a heater of a recording head is rapidly heated, thereby generating bubbles in a liquid on the heater to cause a rapid volumetric increase of the liquid. A droplet of the liquid is ejected from an orifice of the recording head by the working force based on this rapid volumetric increase and applied to a recording medium, thereby conducting printing.
According to this system, however, a scorch deposition (the so-called kogation) of an ink may be built up on the surface of the heater in some cases as the result of the repeated heating of the heater of the recording head for ejecting the ink upon mass printing. In some cases, the build-up of the scorch may involve a problem that thermal energy cannot be effectively transferred from the heater to the ink, so that the quantity of the droplets ejected and the velocity of the droplets ejected are reduced compared with the initial printing, which adversely affects the quality of images formed. When it is intended to continuously achieve high-quality printing in this case, it is necessary to change the recording head. Such circumstances lead to increase in printing cost for users as a whole. Accordingly, achieving more reduction in kogation on the heater, which has a possibility of causing such circumstances, so as to more lengthen the life of the recording head is always an important technical problem to aim at a further improvement in the bubble-jet system.
For example, Japanese Patent Application Laid-Open No. 3-160070 has proposed an ink comprising an oxo anion. As examples of the oxo anion, are mentioned phosphates, polyphosphates, phosphoric esters, arsenates, molybdates, sulfates, sulfites and oxalates.
In view of the above technological background, an object of the present invention is to provide an ink for ink-jet recording capable of reducing kogation on the surface of a heater for applying thermal energy to an ink in a recording head to eject the ink from the recording head.
Another object of the present invention is to provide a method for alleviating scorch deposition on the surface of a heater for applying thermal energy to an ink in a recording head to eject the ink from the recording head.
Further object of the present invention is to provide an ink-jet recording apparatus which permits higher-quality printing and the achievement of a more lengthened life of a recording head.
A still further object of the present invention is to provide a recording unit which permits high-quality printing over a long period of time.
A still further object of the present invention is to provide a method for lengthening the life of a recording head to achieve further reduction in printing cost while providing high-quality prints.
The above objects can be achieved by the present invention described below.
According to a first aspect of the present invention, there is provided an ink for an ink-jet recording used with an ink-jet recording apparatus comprising an ink-jet recording head provided with a heater having an outermost protection layer comprising at least one of a metal and an oxide thereof, the ink-jet recording apparatus ejecting the ink by utilizing thermal energy, the ink comprising (a) colouring material; (b) liquid medium; and (c) at least one selected from the group consisting of polyolphosphates and salts thereof.
According to another aspect of the present invention, there is thus provided a method for alleviating scorch deposition on a surface of a heater of a recording head of an ink-jet recording apparatus, the heater being arranged to apply thermal energy to an ink in the recording head to eject the ink from an orifice of the recording head, and the heater having an outermost protection layer containing at least one selected from the group consisting of a metal and a metal oxide, wherein the ink comprises (a) a colouring material; (b) a liquid medium; and (c) at least one selected from the group consisting of polyolphosphates and salts thereof.
According to this constitution, the kogation on the outermost protective layer of the heater can be extremely effectively reduced. The reason why such an effect is brought about by using such an ink is not clearly known. However, it is considered that at least one selected from the group consisting of polyol phosphates and salts thereof in the ink interacts with the metal and/or the metal oxide making up the outermost protective layer of the heater to prevent kogation or facilitate decomposition of scorch and separation of scorch from the heater surface.
When the metal contained in the outermost protective layer of the heater is tantalum, or the metal oxide is tantalum oxide, the effect becomes more noticeable. Supposing that the quantity of energy applied to the heater is Eop, and the threshold quantity of energy applied to the heater, which is required to eject the ink, is Eth, the kogation-preventing effect of the present invention becomes far excellent when the quantity of energy applied to the heater is preset in such a manner that Eop meets the relationship
1.10xe2x89xa6Eop/Eth less than 1.60.
According to further aspect of the present invention, there is also provided an ink-jet recording method comprising the steps of applying pulse electric signals to a heater in an ink flow path according to recording signals, generating heat from the heater to heat ink in the ink flow path and ejecting ink from an orifice, wherein the ink comprises (a) colouring material; (b) liquid medium; and (c) at least one selected from the group consisting of polyolphosphates and salts thereof.
According to further aspect of the present invention, there is provided an ink-jet recording apparatus comprising: an ink container containing an ink; an ink-jet recording head having a heater for applying thermal energy to the ink within an ink flow path, the ink being fed from the ink container, and means for applying a pulsed electric signal in response to recording information, the heater being provided with an outermost protection layer containing at least one selected from a metal and a metal oxide, wherein the ink comprises (a) colouring material; (b) liquid medium; and (c) at least one selected from the group consisting of polyolphosphates and salts thereof.
According to still another aspect of the present invention, there is provided a recording unit comprising an ink container containing an ink, and an ink-jet recording head for ejecting the ink from an orifice by thermal energy, the ink-jet recording head having a heater for applying thermal energy to the ink, and the heater being provided with an outermost protection layer comprising at least one selected from the group consisting of a metal and a metal oxide, wherein the ink comprises (a) colouring material; (b) liquid medium; and (c) at least one selected from the group consisting of polyolphosphates and salts thereof.
According to still further aspect of the present invention, there is provided a method for prolonging a life of a recording head equipped with a heater, the recording head being used in an ink-jet recording method comprising a step of ejecting an ink through an orifice by applying thermal energy to the ink with the heater, the heater being provided with an outermost protection layer comprising at least one selected from the group consisting of a metal and a metal oxide, wherein the ink comprises (a) colouring material; (b) liquid medium; and (c) at least one selected from the group consisting of polyolphosphates and salts thereof.